During the manufacture and processing of tobacco products, by-products such as tobacco stems, leaf scraps, and tobacco dust produced during the manufacturing process (including stemming, aging, blending, cutting, drying, cooling, screening, shaping and packaging) are produced and can be recycled to reclaim their useful tobacco content. For example, tobacco stems and tobacco fines from manufacturing processes are unsuitable for use directly in the manufacturing of tobacco products. Since the stems and fines represent a substantial amount of raw material investment, processes have been developed to further convert these stems and fines into products such as reconstituted tobacco sheets which are then useable in relatively large amounts in a mixture with acceptable processed tobacco leaf. “Reconstituted tobacco” is manufactured in a slurry or cast sheet process wherein pulp of mashed tobacco stems and other parts of the tobacco leaf are ground and mixed with a solution that might contain different additives. The resulting tobacco slurry is then sprayed to form a thin film, dried, rolled and diced into strips which are added to a filler.
Nitrosamines are organic compounds found in many consumer products, such as tobacco, food products and cosmetics. Nitrosamines have drawn intense scientific interest because some of the compounds in this class have been shown to be carcinogenic in laboratory animals. It has been reported that air-cured and flue-cured tobaccos contain tobacco specific nitrosamines which can be found in smokeless tobacco, mainstream smoke and side stream smoke of cigarettes. In tobacco, four species of nitrosamines are produced at appreciable quantity. These are 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, N-nitrosonornicotine, N-nitrosoanatabine, and N-nitrosoanabasine. Tobacco specific nitrosamines are not considered to be present in significant quantities in growing tobacco plants or fresh cut tobacco (green tobacco), but can be formed during the curing process. In addition to the formation of tobacco specific nitrosamines during the curing process of green leaves, tobacco specific nitrosamines may also be formed during processes used to prepare aqueous tobacco slurries—such as processes used to prepare reconstituted tobacco.
In an attempt to reduce tobacco specific nitrosamines, various treatments of tobacco plants or harvested tobacco leaves have been suggested, including radiation treatments, chemical treatments and extractions. Other methods for reducing tobacco specific nitrosamines have been suggested by MacKown et al. (1988) J. Agric. Food Chem. 36, 1031-1035. these methods are treatment by sterilization, with microbial inhibitors, with bases to increase pH, or with ascorbic acid to decrease the accumulation of tobacco specific nitrosamines during the production of reconstituted tobacco sheets. However, MacKown et al. (1988) only considered the formation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (abbreviated as NNK), N-nitrosonornicotine (abbreviated as NNN) and N-nitrosoanatabine (abbreviated as NAT) in their study. Moreover, whilst the authors considered the effect of pH on the levels of these compounds in tobacco slurries, no significant difference was seen in the level of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone during the treatments.
A need currently remains for an effective and cost efficient method for reducing tobacco specific nitrosamines, particularly those tobacco specific nitrosamines that are formed during the preparation of tobacco homogenates—such as aqueous tobacco slurries. In particular, there is a need for a method that can be used to reduce all four species of tobacco specific nitrosamines in tobacco homogenates (that is, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N-nitrosonornicotine and N-nitrosoanabasine and N-nitrosoanatabine).